The present invention relates to positioning devices for positioning disk-like workpieces with respect to a processing tool to be applied to the workpiece. The present invention is particularly useful for centering semiconductor wafers with respect to a monitoring/metrology/inspection tool.
It is often the case in the manufacture of various workpieces that the workpiece needs to be precisely positioned (registered) prior to being processed by a processing tool. For example, during the production of semiconductor devices, the semiconductor wafers progress on a production line being transported to various stations for processing, inspecting and the like procedures. During inspection/measurement, it is essential that the semiconductor wafer, which is of circular disk shape, be precisely centered with the center of an inspection area defined by the inspection/measurement tool.
One kind of conventional xe2x80x9ccenteringxe2x80x9d assembly for positioning disc-shaped workpieces comprises a support base formed with a chuck in the center region thereof, a pair of stops in a mutually confronting state, and a shifting mechanism for moving the stops in directions perpendicular to the direction of the entrance of the workpiece. The mutually confronting contact surfaces of the stops are concave and are of semi-circular shape with the curvature radius being equal to the radius of the workpiece to be processed. When a workpiece is fed to this centering mechanism and its center approaches the center of the chuck, the workpiece is contacted by the semi-circular contact surfaces of the stops approaching from their movable directions, and is thereby clamped and centered. In a conventional rotational processing device with the above-described centering mechanism, the radius of curvature of the semi-circular contact surfaces of the stops is of a certain fixed value corresponding to a predetermined workpiece type (i.e., diameter).
Another example of a conventional technique of the kind specified is disclosed in U.S. Pat. No. 5,171,031. This patent discloses an apparatus for fabricating a semiconductor device, utilizing a wafer rotating processing device provided with a centering assembly. The centering assembly comprises: a plurality of movable stops, which are disposed with even angular spacing around the center of a wafer chuck and are movable radially towards and away from that center to thereby clamp the periphery of a wafer conveyed onto the chuck and subsequently release the same. A plurality of pairs of wafer position sensors is disposed at spaced-apart positions in a single row along the path of advance of the wafer. The sensors of each pair are disposed on opposite sides of and equidistant from the chuck center, each sensor operating to detect whether or not a part of the wafer exists thereabove and to generate a corresponding output signal.
Yet another centering assembly was developed and is used in Integrated Thickness Monitor System NOVASCAN 420, commercially available from Nova Measurement System Ltd., Israel. This centering assembly comprises two supporting beams or jaws of concave and of semi-circular shape with a curvature radius equal to that of the wafer to be processed. The supporting beams are linearly movable toward and away from that center of the wafer and abut with the outer circumferential periphery of the wafer. While the supporting beams move towards their closest positions, they push the wafer between them. Since the center of the circle defined by the two supporting beams is aligned with the center of the measuring position, once supporting beams arrive at their final position, the center of the wafer will be at the desired location.
The above centering techniques have some drawbacks. These assemblies demand an additional footprint, and cannot be easily integrated within various processing tools. The mechanical drivers of registration members and registration members (stops or jaws) themselves occupy a large area and limit access to the working space therebetween. Since registration is provided by linear movement of the registration members, relatively complicated mechanical transmission is required. Furthermore, the sealing of linearly movable shafts is a difficult technical problem by itself.
There is accordingly a need in the art to facilitate precise positioning of a workpiece with respect to a processing tool, by providing a novel positioning assembly that provides a simple and effective solution for the above problems of the conventional devices of the kind specified.
It is a major feature of the present invention to provide a simple and reliable assembly for positioning a substantially disk-shaped workpiece in a registered position.
It is a further feature of the present invention to provide a positioning assembly, which can be readily retrofitted to existing machine tools.
It is a still further feature of the present invention to provide such an assembly that permits a convenient, quick and simple change-over from one diameter setting to another, being thereby readily adjustable to different sizes of workpieces.
The main idea of the present invention consists of the following. At least three spaced-apart guiding members are used to define a support plane for supportingly engaging the circumference of a workpiece at three spaced-apart locations. Each of the guiding members is mounted for pivotal movement between its two extreme positions in the support plane. The pivotal movement of the guiding members, when engaging the workpiece, results in pushing the latter until it reaches the desired position. The correct position of the workpiece corresponds to the tangential alignment of each of the members with respect to the circumference of the workpiece.
There is thus provided according to the present invention, a positioning assembly for positioning a substantially disk-shaped workpiece in a registered position, the assembly comprising at least three spaced-apart guiding members, which define a common support plane for supporting the work-piece and are capable of engaging the circumference of the workpiece at three spaced-apart locations, wherein each of said guiding members is mounted for pivotal movement in said support plane between its two extreme positions, the movements of the guiding members transport the workpiece towards said registered position.
The workpiece, when in the registered position thereof, is located within a working area of a processing tool, and the registered position is defined by the coincidence of an axis of the workpiece and a predefined location in this working area. The processing tool may be an inspection, metrology, monitoring or the like.
Preferably, each of the guiding members comprises a supporting portion and a guiding edge. The supporting surface is slightly inclined relative to the support plane, and engages the workpiece from below at a small segment of the workpiece circumference, while the guiding edge is substantially perpendicular to the support plane. The guiding edge may be such as to springingly support the circumference of the workpiece, for example, being in the form of a projection from the support portion.
Preferably, the length of the guiding member is variable, for example, it may be designed from two telescopically connected parts.
The positioning assembly may comprise at least three pairs of guiding members, the members of each pair being vertically aligned, so as to support two workpieces.
According to another aspect of the present invention, there is provided a processing tool for processing substantially disk-shaped workpieces, the processing tool being associated with a positioning assembly for positioning the workpiece in a registered position with respect to the processing tool, wherein the positioning assembly comprises at least three spaced-apart guiding members, which define a common support plane for supporting the workpiece and are capable of engaging the circumference of the workpiece at three spaced-apart locations, each of said guiding members being mounted for pivotal movement in said support plane between its two extreme positions, such that the movements of the guiding members transport the workpiece towards said registered position.